Large mining and construction trucks have different driving characteristics than on-highway vehicles. One primary difference results from the size and mass of the truck. For example, many trucks now in production have a haul capacity of 370 tons. When operating a truck with this much mass it is important to control its speed especially when travelling down a grade.
Large mining and construction trucks are expensive to maintain if not operated properly. To reduce the wear on a truck's service brakes an experienced operator will use the transmission and engine to retard vehicle speed when travelling down an incline. Thus, when an experienced operator approaches an incline the operator will determine an appropriate gear based on the apparent grade of the slope and downshift into that gear. Then, when the truck enters the incline, the transmission and engine will create a retarding effect that will help prevent the truck from increasing speed and thereby requiring the operator to apply the service brakes to maintain the desired vehicle speed. If the operator chooses an inappropriate gear or the grade of the slope increases, the vehicle speed may begin to increase. An experienced operator will apply the service brakes to decrease engine speed to a shift point and downshift to the next lowest or a lower appropriate gear. Less experienced operators may use the service brakes to maintain a desired vehicle speed, which will reduce the life of the service brakes and increase the operating cost of the truck.
It would be preferable to have a system that could automatically operate the vehicle to control vehicle speed while travelling down an incline, in a manner approximating the effects of an experienced operator.